1. Technical Field
The present invention relates to a transmission-type display such as a head mount display that presents an image formed by an image display element or the like to an observer.
2. Related Art
In a transmission-type display such as a head mount display (hereinafter, also referred to as a HMD) that is mounted on the head of the observer, development of augmented reality sensation (hereinafter, also referred to as AR or augmented reality) in which image light is superimposed on a world that is viewed in the real field of view is expected. For example, a technique of determining a distance to an object of interest of the user by using a focusing mechanism of a camera such that the position of the image is consistent with the position of the real world, and performing an image shift of an appropriate amount on the image that is displayed on the display device provided in front of the eye, in order to make a modification on the difference between the positions of the camera and the eye of the observer has been known (see JP-T-2013-537784).
Here, although the see-through type HMD is roughly divided into a single-eye type HMD that projects the image light to one eye, and a both-eye type HMD that projects the image light to both eyes, since humans estimate the distance from the image light to be projected in the single-eye type, it is considered that there is a case where it is difficult to feel the sense of distance. On the contrary, in the both-eye type HMD, since the distance of the image light is felt more accurately by displaying the image light (an image with a parallax) adjusted to the left and right eyes, it is possible to cause the wearer of the HMD (observer) to experience the world of a more realistic AR. For example, for the purpose of assistance in a work site or the like, development of the HMD corresponding to the AR has progressed in recent years.
However, in the case of performing visual recognition corresponding to AR by using the parallax generated by projecting different images to the left and right sides at the time of binocular vision, a so-called contradiction between the convergence and the focus adjustment of the eye (hereinafter, referred to as regulation) occurs. In the case of binocular vision, what has an important role in understanding the sense of distance of the image light is an angle of convergence which is the angle formed by the display object and the right and left eyes. In general, if the actual object is placed close to the eye and is viewed, the angle of convergence increases; in contrast, if the actual object is placed far from the eye and is viewed, the angle of convergence decreases. Since a parallax is generated by forming images which are deviated in the left and right direction by shifting an image through a software correction process, by using the above fact, and changing the angle of convergence of the eye of the observer, pseudo stereoscopic vision is possible. In the case of changing the angle of convergence in this manner, if the image distance, that is, the display position of the image light is not changed and maintained, only by performing a correction process of the image, without performing an optical process such as changing the focal distance, the regulation maintains constant and it becomes a state where the angle of convergence and the regulation do not match. Therefore, if the shift amount of the image is particularly great, a problem in contradiction between the angle of convergence and the regulation increases, and there is a concern that fatigue of the observer becomes significant. In particular, in the case of processing the AR at a work site, it is considered that it becomes a major problem.